This invention relates to an independently retractable, double bladed, utility knife.
Utility knives with retractable blades have been used in a variety of applications for many years. These blades suffer from several shortcomings in certain applications. For example, in the roofing trade it is generally necessary for a roofer to carry two separate utility knives. One knife is equipped with a straight razor blade for cutting felt paper and the like, while the other knife is equipped with a hooked blade for cutting shingles which have a granulated surface. Neither of these knives is well adapted for cutting the other type of material. As a result, it is often necessary to switch knives. To accomplish this, the user must retract the first blade and put it away before retrieving the second knife and extending its blade. This is inconvenient and inefficient, as it must be repeated again and again during the workday.
There have been prior attempts to solve this problem. For example, U.S. Pat. No. 719,208 to Garda relates to a plurality of blades and a fork attached to a common handle which are pivotable in relation to each other to allow for individual use. U.S. Pat. No. 1,599,800 to Van Sickel discloses adjustable parallel blades extending from a common holder. U.S. Pat. No. 5,093,994 to Karas and U.S. Pat. No. 5,960,544 to Beyers disclose double bladed utility knives. These knives have a blade at opposite ends. To switch blades, the first blade must be retracted, the knife turned in the hand and the second blade extended. U.S. Pat. No. 4,578,865 to Keller relates to a double bladed utility knife having concurrent advancement and retraction of the blades. These attempts suffer from the inconvenience and inefficiencies associated with the use of two separate knives, since in each case to switch blades, the user must retract, manipulate the knife, and extend blades, switch blades entirely or again use two knives.
U.S. Pat. No. 5,337,481 to Mears discloses an invention which improves on the prior art but which has additional shortcomings. Mears discloses a double bladed utility knife which has parallel, individually retractable blades which extend from one end of the knife and are operated by a retraction mechanism located on the top surface of the blade housing. In use, the roofer must apply pressure to the knife to allow the blade to cut the roofing material. The only surface available for applying such pressure is the top surface of the blade, causing the retraction mechanism to injure the users"" fingers or at least reduce the amount of pressure available to be brought to bear on the blade. In addition, the Mears"" utility knife is longitudinally oriented to form a rectangular shape. This orientation does nothing to improve the ease of use, especially when combined with the placement of the retraction mechanism on the top surface of the knife.
None of these prior inventions features a utility knife with a pair of independently extendable blades at one end of the knife, which is ergonomically designed and oriented to be easily operable with one hand by a mechanism on the side of the knife, as well as safe, convenient and economical.
This invention provides a unique utility knife, which has two different parallel blades. The blades are independently extendable and retractable from one end of the knife by a simple mechanism located on the side of the knife.
More specifically, this invention consists of two handle parts, which are parallel to each other and are essentially mirror images of each other. Placed between these two handle parts and separating them is a central handle part. These parts are all pierced by openings, which are aligned in a way that allows passage of an attachment means. The attachment means maintains proper alignment of the utility knife and enables the parts to be joined or separated in order to replace the blades. In addition to attachment openings, a slot pierces the two handle side surfaces to allow passage of the lever for extending and retracting the blades.
In one of the preferred embodiments, the handle parts are essentially longitudinally oriented to form a parallelogram. In a second preferred embodiment, the handle assembly is shaped so that the two blades disposed therein are offset from the main, longitudinal axis of the handle parts to form an angle which reduces strain on the user.
The handle parts have an external surface with which the user comes in contact, a front through which the cutting blades pass, a rear opposite the front, a top surface on which the user applies pressure to cut, and a bottom surface contiguous with the cutting surface of the blades.
Inside the knife are two depressions, one in each handle part, each of which contains a slidable blade holder and a cutting blade. These depressions begin as openings on the front of the knife and extend inwardly towards the rear. Attached to the slidable holder is a lever, which extends through a slot in the handle to the exterior, allowing the user to operate the blades. These levers are disposed on the side surfaces, also called the external user surfaces, of the handle parts to allow the user to apply pressure more effectively to the utility blade cutting edges.
The central handle part has two raised tracks on each side which are parallel to each other as well as the top and bottom of the central handle part and extend inward perpendicularly from the front of the knife. These tracks match the two depressions, one in each handle to hold the blade holder and blade in position.
Accordingly, it is the object of the present invention to provide an improved utility knife having double blades so that a user may carry and use one knife instead of two. Another objective of the present invention is to provide a double bladed utility knife, which requires no manipulation other than extension or retraction of the blades by simple movement of the fingers. Yet another objective of the present invention is to provide a retraction mechanism placed in such a way as to allow maximum pressure to be exerted on the knife and hence, the blades, without causing pain or added exertion to the user. Still another objective of the present invention is to provide a more ergonomically correct utility knife by improving the orientation of the handle parts.